Structural and physical characterization of NpPt₂In₇

Abstract

A new neptunium intermetallic compound, NpPt2In7, has been synthesized in polycrystalline form and characterized by several macroscopic techniques. A Rietveld analysis of its powder X-ray diffraction pattern shows that NpPt₂In₇ crystallizes in a tetragonal lattice with I4/mmm symmetry and lattice parameters a = 4.58471 (3) Å, c = 21.5065 (3) Å. Magnetic susceptibility, electrical resistivity, Hall effect, and heat capacity measurements indicate a metallic character and the occurrence of antiferromagnetic order below a N eel temperature TN ¼ 23 K. The transition is exceptionally robust and TN decreases by 0.2 K under a magnetic field of 9 T. A modified Curie-Weiss fit of the high-temperature magnetic susceptibility curve x (T) gives an effective magnetic moment meff ¼ 2:54 mB close to the value expected for trivalent Np. Low temperature heat capacity measurements give a reduced Sommerfeld linear coefficient close to 25 mJ mol 1K 2 and a Debye Temperature QD = 181 K. First principles, correlated-band electronic structure calculations suggest that the neptunium magnetic moment in NpPt₂In₇ is localized and that a quasi-two-dimensional antiferromagnetic structure could result from the competition of very weak interlayer interactions leading to very anisotropic properties.